Ensure git is installed in prepare-workspace-git role

Since this role relies on git, let's ensure git is
installed. Issue got detected when git was made
build-only in [1], it's now being reverted[2].

[1] https://review.opendev.org/#/c/745678/
[2] https://review.opendev.org/#/c/747025/

Related-Bug: #1892326
Change-Id: I3115d581aa3bb8b22db1cd10e4180e8cc0e530f4

roles/prepare-workspace-git/tasks/main.yaml

@@ -1,3 +1,9 @@
+- name: Ensure git is installed
+  package:
+    name: git
+    state: present
+  become: yes
+
 - name: Find locally cached git repos
   stat:
     path: "{{ cached_repos_root }}/{{ zj_project.canonical_name }}"